This invention relates to an apparatus for feeding sheets of media from a stack of the media. In particular, this invention relates to an apparatus for feeding porous sheets of a media from a stack of such sheets.
The applicant has developed various printheads which provide high speed, photographic quality printing. The printheads comprise ink jet nozzles arranged in an array. The ink jet nozzles are formed using microelectromechanical systems (MEMS) technology. The use of MEMS technology results in very high speed printing capabilities where pages can be printed at a rate of up to two pages per second (for double-sided printing).
To facilitate such high speed printing, it is important, firstly, that the paper fed to the printing station of the printer is accurately aligned and capable of the required feed rate with as little likelihood as possible of paper jams or the like, occurring. Secondly, the paper must be able to be fed to the printing station at a rate sufficient to use the high speed printing capabilities of the printing station to its fullest extent.
According to a first aspect of the invention, there is provided an apparatus for feeding porous sheets of media from a stack of such sheets, the apparatus comprising
A retaining structure that is configured to retain the stack in an aligned condition;
A pick-up device that is operatively arranged with respect to the retaining structure, the pick-up device including a gas conduit that is in fluid communication with a gas supply and a nozzle arrangement that is in fluid communication with the gas conduit, the nozzle arrangement being shaped to define a pick-up surface, the pick-up device being displaceable along a feed path relative to the retaining structure, the pick-up device being positioned so that the nozzle arrangement is capable of directing a flow of gas onto a first sheet of the stack such that the gas passes partially through the first sheet and impinges on a second sheet, generating a cushion of air between the first and second sheets to separate the first and second sheets, the gas supply being reversible so that the first sheet can be drawn towards the pick-up surface and retained against the pick-up surface; and
A displacement mechanism that is operatively arranged with respect to the retaining structure for displacing the pick-up device along the feed path so that the first sheet is fed from the stack along the feed path.
The nozzle arrangement may be shaped so that, as the gas flow is applied to the first sheet at a suitable rate, a region of relatively low pressure is generated between the pick-up surface and the first sheet thereby to facilitate displacement of the first sheet towards the pick-up surface.
The apparatus may include a feed mechanism that is operatively positioned with respect to the retaining structure, downstream of the pick-up device for receiving the first sheet from the pick-up device.
The feed mechanism may be in the form of a roller assembly.
The pick-up device may include a pick-up bar that spans the stack of media, the nozzle arrangement being mounted on the pick-up bar and the gas conduit being in the form of an air hose that is attached to the pick-up bar and is connected to the nozzle arrangement.
The displacement mechanism may include an axle that is rotatably mounted with respect to the retaining structure. A motor may be connected to the axle for rotatably driving the axle. At least one arm may be connected to an end of the axle, the pick-up bar being pivotally mounted on the, or each, arm, so that, on rotation of the axle, the pick-bar is displaced along the feed path.
According to a second aspect of the invention, there is provided a method of separating a sheet of print media from a stack of sheets, the sheets being porous and the method including the steps of:
blowing fluid onto a top surface of a topmost sheet of the print media on the stack so that the fluid passes through at least the topmost sheet of the stack; and
capturing at least a part of the topmost sheet for conveyance to a printing station of a printer.
The method may include blowing the fluid on to the top surface of the topmost sheet through an aperture means of a pick-up means of a print media feed arrangement. The pick-up means may be in the form of a pick-up bar. The aperture means of the pick-up bar may be in any of a number of different forms. For example, the aperture means may be in the form of a channel extending longitudinally along the bar. Instead, the bar may support a plurality of longitudinally spaced, discrete orifices, the orifices defining the aperture means.
The method may include, initially, prior to capturing said at least part of the topmost sheet, lifting said at least part of the topmost sheet from the stack. The method may include causing said lifting of said at least a part of the topmost sheet by creating a low pressure region between a face of the pick-up means and the top surface of the topmost sheet of print media.
According to a further embodiment of the present invention there is provided a method of separating a sheet of print media from a stack of sheets, the sheets being porous and the method includes the steps of:
applying high pressure to a fluid to cause said fluid to pass through a topmost sheet of the print media on the stack thereby separating the topmost sheet from the stack; and applying low pressure to the fluid to lift from the stack a part of the topmost sheet.
Preferably, the method includes maintaining the pick-up means in spaced relationship relative to the top surface of the topmost sheet of print media to cause said low-pressure region.
The method may include capturing said at least part of the topmost sheet of print media by the pick-up means, preferably by reversing a direction of fluid flow through the pick-up means to cause a change from a blowing action to a suction action.
The method may include conveying said topmost sheet of print media in a direction substantially normal to a direction of flow of fluid blown on to the stack.